Distinguishing features

Virion

Morphology

Crystal structures of many enteroviruses have been resolved (Enterovirus A: CV-A7, CV-A16, EV-A71; Enterovirus B: CV-A9, CV-B3, E-1, E-7, E-11, E-12, SVDV-1; Enterovirus C: PV-1, PV-2, PV-3, CV-A21, CV-A24v; Enterovirus D: EV-D68; Enterovirus E: EV-E1; Rhinovirus A: RV-A1, RV-A2, RV-A16; Rhinovirus B: RV-B14; Rhinovirus C: RV-C15). CPs 1B, 1C and 1D of the human enteroviruses and rhinoviruses are among the largest in the family (VP1-3 chain lengths, 238-302 aa), and this is reflected in the typically long inter-β-strand loops, the larger than average thickness of the capsid wall (46 Å), and a surface relief that is strongly pronounced compared to most other picornaviruses. Encircling a raised area at the 5-fold axis is a 25 Å deep groove, or "canyon", into which the cellular receptor for poliovirus binds. The binding site for the pocket factor lies beneath the floor of this canyon within the 1D β-barrel. Virions can be converted by a variety of treatments (gentle heating, binding to receptor, or some neutralizing antibodies) to altered ('A') particles of 135S which lack 1A (VP4) and possess altered antigenicity.

Physicochemical and physical properties

Acid stability is variable. The virions of most enterovirus species are stable at pH 3.0, while those of the rhinovirus species are unstable below pH 5-6. Similarly, the buoyant density in CsCl of the enterovirus virions is 1.30-1.34 g cm-3, while the rhinoviruses range from 1.38 to 1.42 g cm-3. Sometimes a small proportion (about 1% of the population) of heavy particles (density: 1.43 g cm-3) can be observed in the enteroviruses. Empty capsids are often observed in virus preparations.

Nucleic acid

Length of genome (Kitamura et al., 1981, Racaniello and Baltimore 1981, van der Werf et al., 1981): c. 7,100-7,450 (5'-UTR: 610-822 nt; ORF: 6,417-6,645 nt; 3'-UTR: 37-99 nt). The genome contains a type I IRES and no poly(C) tract. The cre is located in 2C (EV-A, EV-B, EV-C and EV-D) or 2A (RV-A) or 1D (RV-B) or 1B (EV-C). Sequence identities for different enteroviruses, or between enteroviruses and rhinoviruses are more than 50% over the genome as a whole although it may be greater or less than this for particular genomic regions. The 5′-UTR of human rhinoviruses is shorter (ca. 650 nt) than that of enteroviruses, due to a deletion of approximately 100 nt between the IRES and the translation start site. Some members of EV-C and EV-D also have smaller deletions in this region. EV-E and EV-F have a non-perfect duplication of the first ~100 nucleotides allowing the formation of a second clover-leaf-like RNA structure. EV-G have an insertion of about 30 nt approximately 65 nt from the 5' end of the genome resulting in a longer stem-loop D in the cloverleaf structure. Varying size deletions in the same region have been observed in some of the human enteroviruses.

Genome organization and replication

Genome layout:

VPg+5'UTRIRES-I[1A-1B-1C-1D/2Apro-2B-2C/3A-3B-3C-3D]3'UTR-poly(A)

The deduced polyprotein of enteroviruses ranges from 2,138-2,214 amino acids. Genomes encode no L protein. 2A protein has proteinase activity (2Apro), which is related to the family of small bacterial serine proteases, cleaves the polyprotein at its own N-terminus. Certain hydrophobic molecules that bind to the capsid in competition with pocket factor exert a powerful antiviral action by interfering with receptor binding and/or uncoating. Antiviral, pocket-binding drugs have been described.

Antigenicity

Approximately 75 enterovirus serotypes and 100 rhinovirus serotypes have been classified by means of neutralization of infectivity.

Virus names, the choice of exemplar isolates, and virus abbreviations, are not official ICTV designations.Download GenBank/EMBL query for sequences listed in the table here.

Certain viruses initially reported as novel echoviruses were later shown to have been misidentified. Thus E-8 is the same serotype as E-1, E-10 is now reovirus 1, E-28 is now human rhinovirus 1A, E-22 is now human parechovirus 1, E-23 is now human parechovirus 2. Similarly CV-A23 is the same serotype as E-9, and CV-A15 is the same serotype as CV-A11 and CV-A18 is the same as CV-A13. Hepatitis A virus (genus Hepatovirus) was previously assigned the name enterovirus 72. Human rhinovirus 87 has been found to be a strain of EV-D68. A number of simian viruses (SV), previously listed as tentative members of the genus, have been moved to the genus Sapelovirus, species Sapelovirus B and renamed simian sapelovirus (SSV) 1 (SV2), SSV-2 (SV 49) and SSV-3 (SV16, SV-18, SV42, SV44 and SV45). Simian agent 4 (SA4), SV4, SV28 and A2-plaque virus have been assigned to the species Enterovirus H. Simian enteroviruses N125 and N203 have been placed into a new type, EV-108, which has been assigned to the species Enterovirus J, along with EV-103 and SV6. Type SV-47 remains unassigned to a species. Porcine enteroviruses (PEV) belonging to CPE group I (types 1-7 and 11-13) have been moved to the genus Teschovirus, species Teschovirus A, and renamed porcine teschovirus (PTV) 1-10. The species Porcine enterovirus A (PEV type 8; CPE group II) has been moved to the genus Sapelovirus and renamed Sapelovirus A (serotype porcine sapelovirus 1). The species Porcine enterovirus B (PEV types 9, 10; CPE group III) has been renamed Enterovirus G.